refactor[next]: Use set_at & as_fieldop instead of closure in iterator tests

[tehrengruber]

Blocked by #1648

Small script to do the conversion:

import ast
import sys

def transform_closure_to_set_at(source):
    """
    Transforms `closure(<domain>, <stencil>, <out>, [<arg1>, <arg2>, ...])`
    into `domain = <domain>
    set_at(as_fieldop(<stencil>, domain)(<arg1>, <arg2>, ...), domain, <out>)`.
    """
    # Parse the input expression
    try:
        parsed = ast.parse(source, mode='eval')
    except SyntaxError as e:
        raise ValueError(f"Invalid Python expression: {e}")

    if not isinstance(parsed.body, ast.Call):
        raise ValueError("Expected a function call expression.")

    func_call = parsed.body

    if not isinstance(func_call.func, ast.Name) or func_call.func.id != 'closure':
        raise ValueError("Expected a 'closure' function call.")

    # Extract the arguments from the closure call
    if len(func_call.args) < 3:
        raise ValueError("Expected at least three arguments: <domain>, <stencil>, <out>.")

    domain = ast.unparse(func_call.args[0])
    stencil = ast.unparse(func_call.args[1])
    out = ast.unparse(func_call.args[2])
    args = ", ".join([ast.unparse(arg) for arg in func_call.args[3].elts])

    # Construct the transformed code as a string
    transformed = f"""domain = {domain}
set_at(as_fieldop({stencil}, domain)({args}), domain, {out})"""
    
    return transformed

def main():
    # Read input from stdin until a blank line is encountered
    lines = []
    for line in sys.stdin:
        stripped_line = line.strip()
        if not stripped_line:
            break
        lines.append(stripped_line)
    
    # Combine the lines into a single input expression
    input_expr = " ".join(lines)
    
    # Perform the transformation
    result = transform_closure_to_set_at(input_expr)
    print(result, end="")

if __name__ == "__main__":
    main()